Cathode supported by integral, inwardly extending legs with verticallyturned ends fastened to inwardly oriented end portions of support leads



Oct. 8, 1968 s. L.-PAWL|KOWSKI ET AL 3,405,307

'CATHODE SUPPORTED BY INTEGRAL, INWARDLY EXTENDING LEGS WITH VERTICALLY-TURNED ENDS FASTENED TO INWARDLY ORIENTED END PORTIONS OF SUPPORT LEADS Filed March so, 196'? 3 5 5f) 3/) E m W K 4 A 411+ J i k 2/ Q/ X H 1 i Q n i fL-Q- E INVENTORS /6 STANLEY L. Emu/rows,

Dav/1w L SAY. l/nmvy t. SM/THGALL United States Patent 3,405,307 CATHODE SUPPORTED BY INTEGRAL, INWARD- LY EXTENDING LEGS WITH VERTICALLY- TURNED ENDS FASTENED TO INWARDLY ORIENTED END PORTIONS OF SUPPORT LEADS Stanley L. Pawlikowski, Donald L. Say, and Harry E. Smithgall, Seneca Falls, N.Y., assignors to Sylvauia Electric Products Inc., a corporation of Delaware Filed Mar. 30, 1967, Ser. No. 627,017 2 Claims. (Cl. 313-278) ABSTRACT OF THE DISCLOSURE A self-supporting and self-spacing thermionic cathode structure formed for use in a cathode ray device comprising a transverse portion in spaced relationship with a control grid and supported by a leg at either end thereof. The transverse portion and the legs are of selected lengths and have selected acute angular jointures to produce a resultant thermal movement of the transverse portion that is substantially only longitudinal. The height of the cath ode structure and the spacing between the transverse portion and the control grid remain substantially constant.

Background of the invention This invention relates to cathode emission means for a cathode ray device and more particularly to a rapid warmup thermionic heated cathode that is self-supporting and self-spacing for use in a cathode ray tube electron gun structure.

In electronic equipment utilizing thermionic electron discharge devices, the time required for heater warm-up has long been recognized as an important factor in determining the interim existent between equipment turn-on and operational response. With the advent of substantially instantaneously responsive solid state ancillary components in the circuitry of cathode ray tube display equipment, the warm-up time of the cathode ray tube heatercathode combination became the main deterrent to a shortened initial warm-up interim. In an attempt to shorten this interim, various ribbon type low power directly heated cathodes have been devised and utilized in association with costly and intricately shaped insulative supports and tensioning means. Appreciable contact of the cathode structure with the support means produced undesired heat sinks and prolonged the warm-up period.

Objects and summary of the invention It is an object of the invention to reduce the aforementioned disadvantages and to provide a cathode struc ture that has rapid warm-up characteristics for use in a cathode ray device electron gun structure. A further object is to provide an improved cathode structure having minimized heat conduction therefrom.

The foregoing objects are achieved in one aspect of the invention by the provision of a thermionic cathode structure for use in the electron gun of a cathode ray device. The cathode is formed of a transverse portion which is supported by a connective leg at either end thereof and oriented in spaced relationship with a control electrode. The transverse portion and the legs meet in selected acute angular jointures and are formed of selected length and have selected coefficients of expansion to produce an expansive movement of the transverse portion that is only substantially longitudinal therealong. There is substantially no vertical movement of the cathode structure as the height thereof remains substantially constant to effect a substantially constant spacing between the transverse portion and the control grid.

3,405,307 Patented Oct. 8, 1968 Brief description of the drawings FIGURE 1 is a partial perspective of a cathode ray device illustrating the invention; and

FIGURE 2 is a cross-sectional diagrammatic view showing the essentials of the invention.

Description of the preferred embodiment With reference to the figures, there is shown a cathode ray device 11 which may be one of a number of conventional type cathode ray tubes or other type of electron beam device. In this instance, a cathode ray tube will be considered as an example wherein only the essentials will be shown and described.

As illustrated, the tube has a neck portion 12 wherein the electron gun is oriented, and a face portion 12 wherein the electron gun is oriented, and a face portion 13 wherewith a target or cathodoluminescent screen may be associated.

Capping the neck end of the tube is an insulative wafer 14 having therein a plurality of support and connective leads of which only several are shown including two grid leads 15 and 15' and two laterally spaced apart cathode support leads 16 and 16. The cathode structure 19 is attached thereto and oriented in spaced relationship with the first grid or control electrode 31 of the electron gun which has an aperture 33 therein. The electron gun is not detailed and the grid electrodes may be of shapes other than shown. Also, the cathode support leads may be oriented in a separate insulative wafer removed from the described capping wafer and associated with the first grid structure.

The directly heated cathode structure 19 is formed of a conventional metal ribbon having a known coefiicient of linear expansion such as a nickel-cobalt alloy, for example Cobanic as manufactured by W. B. Driver Company, Newark, NJ. A transverse portion 21, which is positioned in a plane parallel to and spaced from the first grid 31, has an emissive region 23 supported therein in spaced relationship to the first grid aperture 33. The transverse portion has a selected length (2A) which exceeds the distance (d) between the cathode support leads 16 and 16'. Two cathode support legs 25 and 25 which are also of selected lengths integrally extend one from each end of the transverse portion and define a selected acute angular jointure 0 therewith in accordance with the selected lengths of the legs and transverse portion and the specific material utilized. The terminal ends of the legs are afiixed to the cathode support leads at substantially inner areas of attachment, as for example at (D) on lead 16. Since the operating temperature of the cathode, especially that of the transverse portion supporting the electron emissive region, is desirably of a certain level; the amount of expansion of the several substantially straight portions of the cathode structure is determined by their selected lengths and angle of jointure therebetween. These are selected to permit a resultant expansive movement of the transverse portion that is substantially only longitudinal therealong.

Thus, a cathode structure is provided that has substantially constant height (H) which is evidenced vertically between the transverse portion 21 and the area of attachment (B). This in turn effects a substantially constant spacing (K) between the transverse cathode portion and the aperture 33 of the first grid.

In greater detail, the relationship of the lengths of the legs and transverse portion and the angular jointure therebetween can be determined with particular reference to FIGURE 2. In practice it is expedient to pre-form the cathode structures which are then positioned and afiixed in desired spacing with the first grid. Therefore, it is necessary to know the values of the initial acute angles (0) formed between the transverse portion and the legs in order that a proper cathode-to-first grid spacing can be achieved which will remain constant under operational temperature conditions. In the ensuing description a formula for determining the initial acute angle is developed.

The first grid aperture 33 has an axis 35 which, by extension, bisects both the transverse portion 21 and the distance (d) between the cathode support leads to provide a half transverse length (A) and a half support lead distance (C). The selected angular jointure (0) has an initial value at ambient temperature which is related to a right triangular relationship DEF wherein the base is part of the transverse portion (AC) and the hypotenuse is represented by support leg 25 which is initially defined at ambient temperature by the length (B); the angle 0 is formed by the jointure between (B) and (AC). The height of the cathode structure (H) is also the height of right triangle DEF and is considered a constant (H B sin 0). The angle formed between the height (H) and the base (AC) is the right angle (a) of the triangle.

Due to the heat of operation, the cathode portions expand. In the range from ambient temperature (T to an average normal operating temperature (T the transverse section (A) expands by amount (AA), and the leg (B) in the range from ambient (T to operating temperature (T expands by the amount of (AB) to form the larger right triangle DEF.

The amount of expansion for the two sections is expressed as:

AA-=(T T (coefficient of expansion of cathode material/ centigrade) A, and

AB: (T -T (coefficient of expansion of cathode material/ centigrade) B.

As previously mentioned, the height of the cathode structure (H), which is also the height of each triangle, remains constant.

In triangle DEF, (AC) +H =B and in triangle DEF, (AC+AA) +H =(B+AB) By subtracting the second of the above equations from the first and canceling the common terms a value for half the support lead distance (C) is determined:

Since then the initial acute angular jointure between the transverse portion and an integral support leg is expressed as:

A self-supporting and self-spacing cathode structure of the aforedescribed type is fabricated, for example, as follows wherein:

The material is the previously mentioned cobalt-nickel alloy in ribbon form having an approximate width of 0.030 inch, an approximate thickness of 0.001 inch, and a coefficient of linear expansion of approximately .O000ll/ centigrade;

The cathode transverse portion (2A) is approximately 0.160 inch in length, whereof (A) is 0.080 inch;

Each of the leg lengths (B) is approximately 0.080 inch;

The ambient temperature (T is about 25 degrees centigrade;

The transverse portion average nominal operating temperature (T is about 725 degrees centigrade; and

The support leg normal operating temperature (T averages about half that of the transverse portion, or approximately 365 degrees centigrade, due to heat conduction therefrom to the support leads.

0= are cos 9=are cos ZBAB AB AA 2BAA 0=arc. cos. .51862 0 arc cos 0=approximately 5 9 degrees Thus there is provided a self-supporting and self-spacing thermionic cathode structure that exhibits rapid warm-up and utilizes compensating expansive movements therein to maintain substantially constant spacing with the first grid structure to control the cut off voltage of the device. It has been found that the rigidity of support is enhanced when the supporting leg lengths are shorter than the length of the transverse portion. Additionally, utilization of a cathode ribbon having a slight cross-sectional camber or channel elTect also augments structural rigidity.

While there has been shown and described what is at present considered the preferred embodiment of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the scope of the invention as defined by the appended claims.

We claim:

1. In a cathode ray tube in an electron gun having an apertured first grid, a rapid heating ribbon-type thermionic self-supporting and self-spacing electrically conductive cathode structure of substantially constant cross-sectional area formed and mounted on said cathode support leads in spaced relationship to said first grid comprising: i

a substantially straight transverse portion having a given length positioned in a plane parallel to and spaced from said first grid, said transverse portion having an electron emissive region in spaced relationship to said first grid aperture, said transverse portion being of a length exceeding the distance between a pair of laterally spaced apart cathode support leads having inwardly oriented end portions for cathode attachment; and

two substantially straight cathode support legs of equal lengths integrally extending one from each end of said transverse portion toward the other to define a selected acute angular jointure therewith in the range of to degrees, and having vertically turned ends to contiguously conform to substantially inner areas of attachment on said cathode support leads to provide a cathode structure having substantially constant height as evidenced vertically between said transverse portion and said area of attachment to effect a substantially constant spacing between said transverse cathode portion and said first grid aperture; said transverse portion and said support legs being formed of ribbon material having a predetermined coefiicient of expansion with sutficient cross-sectional camber to provide structural rigidity to said substantially straight selected lengths whereof the expansive movements during cathode operation are substantially longitudinal in the respective planes thereof.

2. A thermionic cathode structure according to claim 1 wherein said acute angular jointure (0) is initially expressed by the formula:

said formula being derived from related values determined by the extension of said axis of said first grid aperture to bisect both the transverse portion of the cathode structure and the distance between said cathode support leads to provide a half transverse length (A) 6 are cos and a half support lead distance (C), said selected angular jointure (6) being determined by the intersection of said half transverse portion (A) and one of said cathode support legs (B) which are related in a right triangular relationship whereof said support leg B) is the hypotenuse, said cathode structure (H) is the height which is a constant (H=B sin 0), while the base (AC) is half of said transverse portion (A) minus half of support lead distance (C), additional values relate to said formula wherein:

T is the ambient temperature of A and B respectively,

T and T are the average normal operating temperatures of A and B respectively,

6 AA=(T T (coefficient of expansion of material/ centigrade) A, and AB=(T T (coefficient of expansion of material/ centigrade) B.

References Cited UNITED STATES PATENTS 2,491,995 12/1949 McIntosh et al. 313271 X 10 2,599,395 6/1952 Kohl 313278 ROBERT SEGAL, Primary Examiner. 

